I make a post on measuring temperature with different sensors and an objective : watch the impact of designing a correct box for you IoT you want to put in a Car.

When sun is lighting your windshield it is not a surprise to get high temperature, but did you expect to get up to 90°C when the outside temperature is about 35°C ?

The packaging have a big impact on temperature as this post will detail it.

These graph are representing data captured during different sunny days and I only kept the highest temperature range. Data have been captured every 5 minutes so the different graph are representing about 25 hour of data capture.

This first graph is showing 3 different sensor situations :

• The highest one is a sensors in contact with a closed black box
• The middle one is a sensor in contact with an open black box
• The lower one is a sensor in contact with a closed white box

As you can see, reaching a 90°C temperature is a really possible experience, even in France. The impact of the color of the bow is about 8°C and the most important parameter for this first perspective. The use of the ambiant air to lower the box temperature have an effect but it is less efficient than color (at least for my test prototype)

This other graph show the impact of putting a small isolator (about 4mm) between the black box and the sensor.

• The highest curve is the sensor in contact with the closed black box
• The lowest curve is the sensor using a 4mm isolator with the closed black box

This way you have a positive impact of about 3 to 5°C… when every degrees is important when reaching these level

If we now add two effect : isolator and white box we can same more degrees as this new graph is showing :

• The highest curve is the sensor in contact with the closed black box
• The lowest curve is the sensor using a 4mm isolator with the closed white box

In this situation, temperature saving is about 6 to 10°C.

I’m sure we could make many experimentation with different box and eventually create ventilation or use some heat dissipator to lower the temperature. This last graph show the temperature difference between the warmest sensor touching the closed back box and the around temperature outside the box:

The difference is reaching about 10 degrees in most of the cases and drastically change this over heating risk.